1. Field of the Invention
This invention relates to sorting of oil shale. In one of its aspects, the invention relates to an improved method and apparatus of sorting oil shale wherein ore particles are heated quickly and without ignition of the oil to change the color of nonoil bearing particles.
2. State of the Prior Art
As liquid oil resources become scarce, interest has increased in producing oil from oil shale reserves. It is known that oil shale is mixed with nonoil bearing minerals known as nahcolite. These minerals which are normally a dark brown color similar to the color of oil shale contain mixtures of bicarbonates which, when heated in the presence of air, turn a whitish color. It has been found that such minerals, after heating, can be optically sorted according to color to sort the nahcolite hearing minerals from the oil-bearing minerals.
It has been proposed to heat such minerals by direct or indirect heat. Such heating, while achieving the color change desired, also tends to heat large portions of the ore requiring large amounts of energy, and in some cases, even can cause ignition or oxidation of the oil in the ore-bearing rock. Further, special atmospheric conditions are required to prevent ignition of the oil.